Project: Silver Line Phase III Project (Lessons-Learned No. 2)
Grantee: Massachusetts Bay Transportation Authority (MBTA), Boston
Title: Integrating and updating cost estimate concurrently with design process
Phase(s): Preliminary Engineering
Category: Design Management
Date: May to October, 2008
When completed, Silver Line Phase III will physically connect the Silver Line Phase I with the Silver Line Phase II forming the Silver Line Bus Rapid Transit (BRT) system. Silver Line Phase I, defined as the Washington Street Replacement Service, is BRT service between Dudley Square in Roxbury and Downtown Boston. Silver Line Phase II is also BRT service, consisting of a tunnel extending from South Station to the World Trade Center in the waterfront area, combined with service to and from Logan International Airport.
Silver Line Phase III will consist of a tunnel segment and surface bus-only lanes. The tunnel will run between the existing South Station and Boylston Station along an Essex Street and Boylston Street alignment. Beyond Boylston Station, an underground turnaround loop beneath the intersection of Boylston Street and Charles Street will provide for operational flexibility. The tunnel will continue from the turnaround loop along Charles Street South to a portal located within a revised Tremont Street layout, roughly between Jefferson Street and Church Street. Within the tunnel, direct connections will be provided to existing MBTA Green Line and Orange Line transit services at Boylston and Chinatown Stations, respectively. A power mode change will occur at the mouth of the transition ramp on Tremont Street before Marginal Road, where the vehicle will switch between electric overhead catenary and its own power system. Outside the tunnel the BRT vehicles will operate in contra-flow bus only lanes with traffic signal prioritization along Marginal Road and Herald Street between Tremont Street and the existing BRT lanes along Washington Street. The Silver Line Phase III will also provide signal priority for the BRT operations on surface streets.
In a typical design development process, the cost estimate usually begins after the design is fully developed and drawings are completed at certain design development stages. Drawings, design reports, and assumptions are then turned over to the cost estimating group to quantify the cost based on parameters such as material pricing, quantities, production rate and labor cost, and equipment. This process usually takes several weeks or months depending on the complexities of the project.
With time constraint, one of the processes that was utilized in the Silver Line Phase III Project was to integrate the cost estimate process concurrently with the design effort on a real-time basis.
Throughout the conceptual design and preliminary engineering phases, a team of cost estimators and designers work together at the early stage of the conceptual design level to develop approaches and assumptions of design elements and quantities. Since certain scope or design details were not yet developed, the cost estimators needed to provide a more general approach to capture the intent of designers. The designers and estimators work together to develop assumptions based on engineering judgment, construction knowledge, and experiences. Provisions were needed to set aside those elements that have yet to be designed, detailed, and quantified by various groups of designers, and incorporated in the future for refinement and adjustment as the design progressed. Comments and suggestions during the regular estimate review were incorporated into the estimate as necessary.
The integration of cost estimate process concurrently with the design can be applied to most major Transit Capital projects across the nation. It has proven to be a successful method for fast tracking cost estimate and design process while maintaining the functional objectives of the project.